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Dehydrating filament

Discussion in 'Filament' started by Lance Weston, Mar 18, 2021.

  1. Lance Weston

    Lance Weston Active Member

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    I purchased a couple of Sunlu dehydrators. The devices can only set temp and must be reset every 24 hours. It is pretty dry this time of year so I decided to learn how to use with these before spring came. I use humidity strips in the dehydrators and am always at 10% RH. I started with 50C. I noticed that my very pliable filament was gradually getting more brittle by the end of the roll. It never broke and the prints stayed good. I dropped the temp by 5C with each new roll. At 40C the filament stayed pliable through the full roll.

    I can't find much info on Ideal dehydration temp or methodology. Anyone have experience with this?
     
    #1 Lance Weston, Mar 18, 2021
    Last edited: Apr 21, 2021
  2. Lance Weston

    Lance Weston Active Member

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    I had read 40C -> 50C. The problem for me is that at 45C the filament gets brittle by the end of the roll. I have to go down to 40C. The print time is 4 or 5 days. I am trying to figure out what is going on and what it is I should be doing. Any time something is happening that should not be I try to find the underlying cause. I was hoping to find others with practical experience who had resolved this.
     
  3. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Even with low humidity PLA/PLA+ will slowly absorb water from the air (storing it with desiccant is probably the only way to completely avoid it). As it does this it gets brittle. I don't use a dehumidifier specific to the filament, I just run one for the entire workshop and keep it as low as it will go. Does that solve it? Not for me -- but it does make it take longer before it is an issue.
     
  4. Lance Weston

    Lance Weston Active Member

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    It is not humidity. As I had said the humidity is always registering 10%RH. The roll goes straight from the bag to the dehydrator and is printed from the dehydrators for 4 to 5 days until finished, then another roll is put in the dehydrator.

    Over the next few weeks I am going to pay more attention to the brittleness of the filament straight from the bag. There is a possibility that the rolls are not all the same and have a quality control problem. It is so easy to fool myself with this stuff by making assumptions, like: all of the rolls are the same.
     
  5. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Yes, that is entirely possible. Filament can be bad :)
    I have been fortunate and only ever had one roll that was contaminated and that was a generic spool I was using. None of the Taulman or ColorFabb spools have ever been a problem (and they would replace them if they were).
     
  6. Lance Weston

    Lance Weston Active Member

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    None of the filament has been bad, as all the prints look great. I now have a process that has reduced my failure rate to almost zero. Pulling the filament once a day and inserting a .4mm needle was single biggest improvement in print quality I have had. I think that it reduces the back pressure in the nozzle and removes any schmutz that makes it through my oiler. I now am looking to reduce every variable for the most consistent prints. The more brittle filament (I now have to wait to see if brittle from the start) prints identically to the more pliable, it just seems "wrong".

    I have now printed about 35 or 40 of the GST3D rolls and have 60 more. Standardizing on one filament makes things easier.
     
  7. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Yes, "wet" PLA will still print and about the most I can say is that if it is really "soaked" with moisture you will get small steam bubbles in the print. They affect it visually, but not so much structurally.

    If it is getting brittle over time then it is likely due to water absorption (note this is really only true for PLA or variants of PLA -- nylons and others behave quite differently).

    Good luck with sorting it :) Let us know what you find.
     
  8. Lance Weston

    Lance Weston Active Member

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    Not wet 10%RH. It is printed from a dehydrator, so only gets dryer as time goes on. Will keep you up to date. Probably a few weeks to know definitively.
     
  9. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Here are some references -- not saying this is YOUR problem, but general notes for PLA:

    https://www.asensar.com/article/3dprinting/how-to-dehydrate-pla-filament.html

    as this article notes: "Both experts and regular users couldn’t agree on the brittleness causes, with each holding on to their respective arguments. However, chances are, there is more than one contributing cause that makes the PLA filament brittle."

    https://ecoreprap.com/pla-filament-brittle/

    and one more: "Why does PLA filament get brittle and snap? PLA filament snaps because of three main reasons. Over time it can absorb moisture which causes it to reduce flexibility, from the mechanical stress of being curled up on a spool, then straightened out with pressure and generally low quality PLA filament."

    https://3dprinterly.com/why-does-pla-filament-get-brittle-snap-fixes-solutions/

    There are a lot of articles around this, but it is not an unusual issue. Keep us apprised of what you figure out.
     
  10. DavidR

    DavidR Member

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    The Sunlu ones suck. They only get to 55 Celcius. The Esun ones are better. They have a fan that blows on the dessicant (so its active as opposed to passive dehydration--more airflow through the filament = more moisture absorbed). They hit 80C (which is sufficient to dry Nylon). They also have a teflon tube that runs from the unit to keep the line of filament between the box and the extruder from being re-exposed to air. The teflon tube also solves problems related to the Palette machines calibration (if you have one).The price is not that different either.

    Also, you should invest in Esuns vacuum bags. It comes 10 with bags, a handpump, 15 dessicant bags, and 10 moisture indicators to let you know when dessicant needs to be replaced. When you lower the ambient pressure on the filament you shift the equilibrium position and the filament gives off more moisture (Le Chatelier's Principle). Here are links to them on Amazon. Let me know if you wind up ordering it and I can tell you how to modify it to maximize compatability.

    Amazon.com: eSUN eBOX 3D Printing Filament Storage Box, Filament Storage Holder, Spool Holder for 3D Printing Filament Dehydrating, Weighing and Keeping Filaments Dry (US Power Supply): Industrial & Scientific



    Amazon.com: eSUN 3D Printing Filament Vacuum Storage Kit, Spool Storage Sealing Bags Dust Proof Humidity Resistant for Keeping Filament Dry, 10 Vaccum Bags / Kit, 33 x 40cm: Office Products.


    On the subject of consistent prints. The biggest problems to solve within your control are leveling, thermal conductivity, and filament getting stuck to the nozzle. For Buildtak sheets the IR leveling is extremely inconsistent, and effectively worthless with PEI. You can improve leveling by using M48 to get a mean value of 8 readings for each mesh point, or if you level each mesh point manually you can get extreme accuracy (to within +/- .005 mm). I have some macros setup in the custom control editor plugin (comes already installed on R2) if you are interested. Just make sure to enter M420 S1 after homing because homing will disable the bed leveling algorithm. For thermal conductivity, I use splice engineering's boron nitride paste, which you use to coat the hole in the heat block the heating cartridge goes into. I also use Nickel-Plated Copper nozzles (this will help with stickiness as well). My nozzle temperature never varies more than 0.3 C (and generally stays within 0.1C). Its a flat line on the temperature graph. For stickiness I will either use splice engineering's "plastic repellent plate" (which is a Teflon nanosuspension stable up to 290C) or I'll apply a Tungsten Disulfide coating. I also print off 25mm calibration cubes pretty religiously and measure the wall thickness with a micrometer to make sure my flow is on point.

    Here are further links to some of what I mentioned above:

    Boron Nitride Paste: Amazon.com: Industrial & Scientific

    Amazon.com: Slice Engineering Plastic Repellent Paint: Industrial & Scientific

    Amazon.com: 1pc 500℃ M6 Plated Copper Nozzle 0.4mm Durable Non-Stick High Temperature for 1.75mm Mosquito hotend V6 hotend Prusa i3 MK3 MK3S BLV MGN Cube 3D Printers (0.4mm): Industrial & Scientific
     
    #11 DavidR, Mar 20, 2021
    Last edited: Mar 20, 2021
    mark tomlinson likes this.
  11. DavidR

    DavidR Member

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    Also, while we are on the subject of measurements, RH is not an ideal metric to gauge how well the dehydrator is working, especially if you are using it while the unit is on. For one thing, if you are using strips that involve a color-changing indicator, (e.g. cobalt (II) chloride), they tend to work via the color-change accompanying the formation of a hydrate. The standard method to obtain an anhydrous salt from one of its hydrates is to heat it. So your measurement will be inaccurate. Put simply, the heat dries out the strip just as it does the filament. The other reason RH is not a good metric is it is telling you how much moisture is in the air, not the filament.
     
  12. Lance Weston

    Lance Weston Active Member

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    I do not use auto leveling. I level the bed with a dial gauge. I had posted how to make dial gauge that clips onto the head. My prints prints are always level and I have no problem with that. Auto leveling did not give me the accuracy I need. I need to be within .02mm for a good finish on the bed side of the print. I put in commercial end stop switches to deliver that repeat-ability.

    I use the Flexplate system, for flatness I put glass with plating . I drill a hole in the R2 bed where the current thermistor is and insert a new thermistor up to the flexplate. I solder the thermistor to traces for the old thermistor. This raised the temp that the glass would get up to by moving the sensor closer to the glass. When the glass eventually wears out I put 1/32" G10 on top of it. The G10 is my most durable surface. I am only using PLA so I need 40C. I get this by setting the temp of the bed to 50C. I verify this is close by using an infrared temp gun. So far this temp is non critical for me, settings of 50C to 70C work equally well. I machine my own solid brass heater blocks. The increased thermal mass works well for me and I never get the leaks associated with aluminum blocks. I modified the code to allow different smoothing factors for the bed and the heater block and then optimized for each. This improved the regulation, but the real limiting factor is that the temp sensors for the block run in the same cable as the extruder stepper. On one machine I removed the block sensor wiring from the cable and my regulation became +/- 0.1C. I did not pursue it because I found temp regulation on the head not to matter. A 1 or 2C regulation worked just as well.
     
  13. Lance Weston

    Lance Weston Active Member

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    I started out using a modified food dehydrator. I printed out parts that let the filament feed directly from the food dehydrator. I used an old dehumidifier RH control mounted in the food dehydrator to turn it on and off thus regulating the RH%. The problem was that I ruined a few rolls by setting the temp too high.

    I got the Sunlu dehydrators because I wanted to keep the temp low. My filament goes from bag to dehydrator, then prints to end of roll. For me all I care about is the humidity of the air in the dehydrator because once in, the roll is never removed. I am currently trying to figure out why some of my rolls when removed are somewhat brittle. I do not yet know whether it is manufacturer production tolerances, or a too high temp in the dehydrator. Right now I am logging incoming brittleness, dehydrator temp and outgoing brittleness. I discard rolls as they come to the end. Filament is cheaper than printer time.

    I have found myself consistently jumping to the wrong conclusions because things "seem" reasonable. I am now making an attempt to measure everything.

    The measurement strips are my only method of measuring RH%. What are you using? I am always looking to improve my setup.
     
  14. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    I use an electronic hygrometer to measure the humidity in the workshop.
     
  15. Lance Weston

    Lance Weston Active Member

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    Does it correlate to the test strips? If not, how far off?
     
  16. DavidR

    DavidR Member

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    I am surprised with all the other "maker" work you seem to do you haven't strayed from PLA into other filaments. The Sunlu is fine for PLA. The strips are fine to use if you are storing filament in the dehydrator and want to make sure that the internal atmosphere stays dry, but you need to seal both the exit holes so that external air doesn't enter the device. This isn't an issue when the unit is on as the hot air raises the internal pressure above external pressure and so air will only escape and not enter while the unit is on. However, once you turn it off, the reverse will rapidly occur (this is known as "suck back"-----the system lost particles of gas and so when returning to room temperature the internal pressure will be less than external pressure). I don't measure humidity as I use indicating dessicants instead. As long as the dessicant isn't saturated the air will be dry. Sometimes I leave them in the empty sunlu unit and when I do they are saturated within a few days, which is why I stress that the filament outlet needs to be blocked if you are storing them in the dehydrator. However, I will stress again, RH really only comes into play when you are maintaining dryness and not when you are drying. To dry the filament, the water molecules adsorbed on the filament need to be in a high-energy state so that they can overcome the intermolecular forces that bind them to the surface of the filament. This is accomplished via convection from dissipated electrical energy (i.e. the energy generated by the heating unit is transferred to the air, and then from the air to the surface of the filament.) the water molecules become energized and jump off the filament in the form of vapor. To keep the vapor from simply resettling on the filament when the surface temp drops back down, you need to have dessicants inside the dehydrator while drying.
     
  17. Lance Weston

    Lance Weston Active Member

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    There is a local guy here Greengate3D that produces PETG in the USA. I was working with him because he was printing really nice looking parts. My problem is that my open frame printers could not produce detailed parts in the PETG. I am sure the problem was on my end because his enclosed printers made made great looking parts.

    I pretty much use the printers for production. After I found GST3D in Miami (made in the USA) whose filament is very strong I decided to pretty much only use their filament. I do not store filament. I buy 20 rolls at a time and have 60 sitting with the printers. I take a roll out of the box, put in the dehydrator and print till done...repeat. I leave the dehydrator on all of the time, right now at 40C with a humidity test strip in the box. The attached poor quality photo shows the sunlu box. I have modified it to put a connector in the rear. I use 6mm OD , 4mm ID tubing to feed the print head. I see no reason to use small ID tubing that can have significant resistance when the filament gets wavy. My goal is keep the printers printing, towards that end I redesign any parts that are prone to failure. The printers are in my basement which does get humid in the summer so dehydrators are needed. How much of what I was blaming on humidity is true I do not know. Only now that I have reliable, consistent printing am I in a position to change variables with some reasonable expectation that the variable I am changing is the corresponding cause of the print quality changing.

    The nozzle problem was one such, as the printer always prints even as the nozzle diameter goes down. The quality change I observe may not bother others. They may believe that is just the way the printer prints and it is okay. My point being that many things we think we know are true, are not true because we have never measured them. I have fooled myself so many times that I now try not to make statements as to why something is happening unless I can measure it and reproduce it.

    I am stockpiling all those parts available only from China. I see political problems brewing that could shut down the supply line. I am trying to develop relationships with made in the USA suppliers for all the parts I can.
     

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  18. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    PET(g or not) can be a challenge to get setup and working on the open-bay models. Not as bad as ABS, but it is a pain since rather than cracking or peeling/lifting (like ABS can) it will also string. Badly. You can fight this with a partial enclosure and retraction fiddling, but I can't say if that would meet your requirements or not even then. Taulman T-Glase is about the only PET type of filament I have had any luck with and it is not applicable to all use cases unless you are painting it. Taulman Tech-G was better than the generics I tried, but even still it had a 'fiddle factor'
     
  19. Lance Weston

    Lance Weston Active Member

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    I ordered a couple of rolls of Taulman as per your recommendation but have not had a chance to print with it, but I will get there. My last 20 rolls of GST3D were $10/roll delivered. It is tough to find a reason to change production when the filament gives excellent results with little failure. I am making another new printer based on the R2, using the basic carriage design and the Partsbuilt boards. The big advantage on my current home-brew is dual z with four posts each 12mm. The bed never needs tinkering and is always stays level across the full 12"x12" bed. The next machine will have much larger rods in the carriage, with a single 10mm rod replacing the two 6mm rods. I think this will be much smoother. It will be my play machine for experimenting with filament.
     

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